This invention relates to material handling devices. More specifically, this invention is a grapple that can be used with robotic or material handling devices for grabbing and holding compliant objects with undefined shapes such as sacks and bags. The grapple of this invention can grab and hold filled sacks from any point on the sack and regardless of the sack orientation and position.
Delivery and postal services across the world currently use sacks to hold letters, magazines and small boxes. These sacks are handled manually by mail handlers in the postal service distribution centers. Most sacks used by the US Postal Service (USPS) do not have eyelets, handles or any form of operator interface for lifting and carrying. The shape, size and the weight of a sack depends on the items in the sack and how it is rested on the floor. During several visits of USPS distribution centers, the inventors have observed sacks that were fully filled with magazine bundles and weighed up to seventy pounds. The heavy weight of these sacks, the lack of handles, eyelets or other operator interface on the sacks, and the unpredictable shape and size of the sacks create awkward and uncomfortable handling situations for U.S. mail handlers at all USPS distribution centers. This awkward sack handling, in particular during repeated maneuvers, increases the risk of wrist, finger and back injuries among mail handlers. To minimize the risk of injuries to workers, the inventors carried out an engineering research effort, on a solid scientific foundation, to design a grapple for grasping and holding sacks. The grapple of this invention grabs and holds a sack regardless of the shape and size of the sack from any point on the sack (i.e. it is not necessary to gather and flatten the edge of the sack or orient the sack prior to grasp.) This invention has been tested and proven to be effective in grabbing and holding sacks.
Inventors have created several devices to hold sacks and bags. For example, Achelpohl, U.S. Pat. No. 4,181,345, describes a manually operated clamping device for lifting filled sacks. The device includes a frame supporting a clamping mechanism. The clamping mechanism includes two spaced parallel bars, mounted at their end to two parallel plates and disposed to be rotated in unison about a common parallel axis by a hand-crank. One of the bars is individually rotatable about its own axis and displaceable towards and away from the other bar. To use the device of Achelpohl U.S. Pat. No. 4,181,345, the gathered top of a filled sack is manually placed between the two bars. The hand crank is manually operated to wrap the top of the sack around the two bars and clamp it between them. Once secured in the clamping mechanism, the combined clamping device and sack may then be lifted by the device""s frame. Although useful for its purpose, the Achelpohl U.S. Pat. No. 4,181,345 device has the disadvantage of requiring considerable manual manipulation of both the sack and the device to accomplish its utility.
To try to overcome some of the disadvantages of the Achelpohl U.S. Pat. No. 4,181,345 device, Achelpohl, U.S. Pat. No. 4,226,458, discloses a device similar to the U.S. Pat. No. 4,181,345 device. In the U.S. Pat. No. 4,226,458 device, the clamping bars are mechanically separable and are mounted only at one end to a frame, such that they form parallel cantilever arms. This allows the gathered ends of a sack to be either inserted or slide between the clamping bars. The end of the sack is then engaged by mechanically operating the clamping mechanism. This device improves the manual operation required of the U.S. Pat. No. 4,181,345 device wherein it is necessary to manually introduce the end of the sack between the clamping bars. Although the Achelpohl U.S. Pat. No. 4,226,458 device has advantages over the earlier Achelpohl U.S. Pat. No. 4,181,345 device, it still requires the gathered end of a sack to be manually placed between the clamping bars, or that the sack be placed on its bottom and the top of the sack gathered and flattened and presented in a proper configuration before the U.S. Pat. No. 4,226,458 device can slideably engage the top of the sack and secure it for lifting.
In another example, Minenko et al., U.S. Pat. No. 4,549,760, discloses a device for gripping and hoisting packed sacks that utilizes a similar mechanism to grab sacks as the Achelpohl U.S. Pat. No. 4,226,458 device and has similar advantages and disadvantages. However in this case one of the bars moves relative to the other one with the help of a hydraulic linear actuator. The Minenko et al. device still requires the gathered end of a sack to be manually placed between the clamping bars. In this case, the sack is placed on its bottom next to the unpowered bar. The second bar, powered by an actuator moves around the first bar causing the throat of the sack to be secured in between the bars.
A later Minenko disclosure, U.S. Pat. No. 4,852,927, describes using two clamping bars to grip and hold the neck of a sack for lifting and transport. The Minenko U.S. Pat. No. 4,852,927 device includes a locking mechanism to secure the clamping bars in a closed position while gripping a sack. Although useful for its intended purpose, the U.S. Pat. No. 4,852,927 device requires that the neck of the sack be manually inserted between the clamping bars and that the device then be further manually operated to close and lock the neck of the sack in the device. Additionally, the sack cannot be released from the device without first removing the load from the locking mechanism.
All of the devices described in the above patents have the following common characteristics:
The gathered and flattened edge of the sack must be carefully placed between two adjacent bars by an operator prior to grasping.
One of the bars rotates around the other one or both bars rotate along a common axis. Then the gathered and flattened edge of the sack wraps around the bars. The weight of the sack itself pushes the rods against each other therefore locks the edge of the sack in between the bars.
It is necessary that the sack be placed on its bottom so it can be grasped by the device""s bars. If a sack cannot be placed on its bottom in a stable form, then the devices described above cannot be used.
In general, a great deal of operator intervention is required for proper and safe operation of the devices described above. This usually results in slow lifting operation and therefore these devices have not been employed in USPS and many other distribution centers where large flow the sacks need to be lifted repeatedly from a shoot or from a conveyor belt.
The basic idea in design of the grapple of this invention is to create a device that allows at least two rollers, powered by at least one actuator, to turn in opposite directions along their own axes while they are pushed toward each other by force of at least one spring. The inward spinning of the rollers and the friction between the rollers and the sack material causes the sack material to be dragged in between the rollers. When the rollers are prevented from spinning, the sack material is kept secure in between the rollers due to the force of spring and friction between the rollers and the sack material. When rollers rotate outwardly, the sack material will come out of the rollers and the sack will be released. This application describes the hardware architecture, the control method and the design issues associated with the grapple.
In view of the above prior art, the object of the present invention is to design a grapple that can grab any point of a sack without any operator intervention and regardless of how the sack is laid on the floor, on a table, or on a conveyor belt. To achieve this objective, an entirely different and effective concept for grasping sacks was developed and is described here. When any of the grapples described in this invention comes in contact with a sack, the sack material will be grabbed and pulled quickly into the grapple without any intervention from the operator. Unlike the devices of the above prior arts, the grapple described here
grabs a sack from any point on the sack.
does not require the edge of the sack to be gathered and flattened prior to grasp.
does not require the sack to be placed on its bottom prior to grasp (i.e. the sack can be laid on the floor or on a conveyor belt from any side.)
does not require operator intervention for grasp.
does not use the weight of the sack to lock and secure the sack in the grapple.